Many compressors, including those used in refrigeration and air conditioning systems, are such that the cooling of its lubricant is required in conjunction with the use of the compressor in a particular application. The need to separate and cool the compressor lubricant in a screw compressor-based refrigeration system is particularly acute given the large amount of oil which is used for various purposes in screw compressors.
The use of system refrigerant for compressor lubricant cooling purposes is advantageous as is heretofore known. In that regard, U.S. Pat. No. 320,308 teaches a refrigeration system in which liquid refrigerant is directed from the system condenser into a separate cooling tank where compressor lubricant is cooled by direct contact with the refrigerant.
U.S. Pat. No. 3,509,731 teaches an air-cooled condenser in which a discrete portion of the condenser is dedicated to lubricant cooling. System refrigerant is directed out of the condenser, into the compressor sump, where it cools the compressor lubricant, and back to the condenser. U.S. Pat. No. 3,548,612 is directed to generally the same subject matter as the aforementioned '731 patent although it teaches the use of an ejector to pump refrigerant from the system condenser to the compressor sump prior to the refrigerant's return to the condenser.
In U.S. Pat. No. 3,820,350 lubricant is directed from an oil separator to a heat exchanger into which liquid refrigerant is directed from a refrigeration system condenser. The liquid refrigerant cools the lubricant and vaporized refrigerant is returned to the compressor at an intermediate pressure location.
U.S. Pat. No. 4,419,865 teaches a screw compressor-based refrigeration system in which liquid refrigerant is directed from the system condenser into a refrigerant receiver. Liquid refrigerant is pumped from the receiver, undergoes a heat exchange relationship with compressor lubricant and is then injected into the compressor discharge line in a metered quantity so as to maintain a constant temperature in the oil-refrigerant mixture discharged from the compressor.
U.S. Pat. No. 4,448,244 teaches a segmented refrigeration system condenser in which system refrigerant passes through a first condenser section, where it is condensed by relatively warmer water, and is then directed into the sump of the system compressor where it cools the compressor lubricant. The refrigerant is next directed out of the compressor to the second portion of the system condenser where it undergoes further heat exchange contact with the condenser cooling water at a location where the water is relatively cooler.
Finally, U.S. Pat. No. 4,558,573 teaches a condenser in a refrigeration system from which liquid refrigerant is drained to a receiver. The receiver and system oil separator are connected to an ejector. The flow of oil from the separator through the ejector draws liquid refrigerant from the receiver with the result that the oil and liquid refrigerant mix in a manner which cools the oil prior to its return to various compressor locations.
The need continues to exist for an efficient and cost effective oil cooling arrangement in a screw compressor-based refrigeration system which avoids the parasitic loss of system capacity typical of previous systems including those where the cooling of compressor lubricant occurs in, or as a result of, heat exchange contact with refrigerant in the system evaporator.